This disclosure generally relates to design and fabrication of optical fiber connectors. In particular, this disclosure relates to hermetic optical fiber connectors for fiber optic sensors used to measure a level of liquid in a reservoir, such as fuel in a fuel tank of an airplane.
Systems for detecting the level of fuel in a tank or compartment thereof using an optical sensor system are known. In some embodiments, the optical sensor system comprises optical fibers installed inside the fuel tank and a light source (e.g., a laser) and optical detectors (e.g., photodetectors) situated outside the fuel tank. In one proposed implementation, light from the external light source is received by a side-emitting optical fiber inside the fuel tank via an optical fiber connector installed in an opening in the wall of the fuel tank. Similarly, light from a pair of side-receiving optical fibers inside the fuel tank is received by the external optical detectors via respective optical fiber connectors. The optical detectors convert the optical data carried by the light from the side-receiving optical fibers into electrical signals. Those electrical signals are communicated to a computer system (also situated outside the fuel tank). For example, the computer system may be a computer or part of a flight control system located on an aircraft. The computer system may be configured to estimate the amount or level of fuel present in the fuel tank or compartment thereof based on the data carried by light propagating through the optical fiber connectors.
As used herein, the term “optical fiber connector” means a connector that optically couples optical fibers to each other. The principal function of an optical fiber connector is to hold a terminal portion of an optical fiber such that the core of the fiber is axially aligned with the optical path of the optical fiber component to which the connector is mated, e.g., so that light from the one optical fiber is optically coupled to another optical fiber. Some optical fiber connectors are designed to mate a terminal portion of one optical fiber with a terminal portion of another optical fiber. To minimize Fresnel loss, the termini of the respective optical fibers should be in physical contact. Typically optical connectors include a “ferrule,” which is a component for holding one or more optical fibers in a state of physical contact such that the fiber ends are optically coupled. As used herein, the term “ferrule” means an elongated body having an axial bore segment configured to support a segment of an optical fiber.
In cases wherein an optical fiber connector passes through a wall of a fuel tank, the optical fiber connector must be hermetically sealed to prevent fuel vapor or liquid leaking out at the interface of the optical fiber connector and the opening in which the connector is installed. One known hermetic optical fiber connector designed for connecting glass optic fibers (GOF) of a GOF fuel level sensor may experience fiber damage inside the hermetic connector. One prior design used an epoxy or glass seal process to achieve hermeticity, which is unable to withstand a large number of temperature cycles and/or a high-vibration environment. In addition, typical hermetic connectors based on prior art require the whole connector on the fuel tank wall to be replaced if the fiber terminus is damaged. A further consideration in the design of a hermetic optical fiber connector is that a new-generation plastic optical fiber (POF) fuel level sensor will eventually replace the GOF fuel level sensor in the future.
It would be desirable to provide a hermetic optical fiber connector that is not susceptible to optical fiber damage or loss of hermeticity and that can be universally used for both GOF and POF fuel level sensors.